1. Field of the Invention
The present invention relates to an optical disc recording and reproducing apparatus equipped with an optical pickup for projecting a laser beam from a laser light source to an optical disc and converting reflection light from the optical disc into a plurality of electric signals via a split optical sensor, through which the apparatus records information on the optical disc and reads information stored in the optical disc so as to reproduce the information. In particular, the present invention relates to an optical disc recording and reproducing apparatus for recording and reproducing information on a digital versatile disk (DVD) having a 0-th layer and a first layer that can record information.
2. Description of Related Art
Conventionally, as for the optical disc recording and reproducing apparatus equipped with an optical pickup for projecting a laser beam from a laser light source to an optical disc and converting reflection light from the optical disc into a plurality of electric signals via a split optical sensor, through which the apparatus records information on the optical disc and reads information stored in the optical disc so as to reproduce the information, a tracking servo method is adopted as a control method for the laser beam emitted from the optical pickup to follow correctly a track formed on the optical disc. A differential push pull (DPP) method is known as this tracking servo method. This DPP method generates a tracking error signal by a computation on output signals of light receiving elements obtained from one main beam and two sub beams.
In order to improve accuracy of the tracking servo using the DPP method, various apparatuses and methods are proposed. For instance, JP-A-2005-228366 discloses an optical disc recording and reproducing apparatus in which a gain value tolerance setting means measures a gain value corresponding to a ratio of levels of a main push pull (MPP) signal and a sub push pull (SPP) signal generated by a tracking error signal computation circuit so as to set a tolerance of the gain value, and an eccentric quantity measuring means measures eccentric quantity of an optical disc so that a gain value of an amplifier is set based on the eccentric quantity.
However, although the above-mentioned optical disc recording and reproducing apparatus can improve accuracy of the tracking servo, intensity of the laser beam to be projected onto the optical disc is different between the reproducing operation and the recording operation. Therefore, if the recording operation is performed at a position of the optical pickup with respect to the optical disc in the direction closing or separating from the position set in the reproducing operation, the accuracy of the tracking servo may be deteriorated.
In particular, if a DVD having a 0-th layer and a first layer for recording is used for recording information, amplitude of the tracking error signal may be decreased due to an influence of interference light from the neighboring layer or the like (see FIG. 8), resulting in unstable tracking servo.